With the development of mobile communication techniques, a mainstream mobile communication network system performs a full range of network coverage in the form of a cellular network, and according to the 3rd Generation Partnership Project (3GPP) TS 23.122, an automatic mode of a mobile terminal after its power on will first select a RegisterePublic Land Mobile Network (RPLMN) which has been successfully registered. If there is no RPLMN in the mobile terminal or the RPLMN is unavailable, the mobile terminal will search for sequentially an appropriate Public Land Mobile Network (PLMN) according to the rules, i.e., firstly search for a Home Public Land Mobile Network (HPLMN) or an Equivalent Home PLMN (EHPLMN), then search for a user-controlled PLMN, and then search for an operator-controlled PLMN, and finally search for other PLMNs available. A home network is determined by an SIM card issued by an operator.
However, with the development of mobile communication techniques and intense competitions in the market, network mergers and network sharing between operators become more and more frequent, and network constructions are sped up. If there are two operators in a country, i.e., operator A having an incomplete network coverage, a weak network capability, or a heavy network load and operator B having a good network coverage, in order to meet market demand, operator A and operator B decide to sign a network resource sharing agreement so that in the case of a same roaming charge, a user is allowed to register preferentially on a network of operator B or register simultaneously on a network of operator A and a network of operator B. However, if a user terminal still searches for a network according to a current protocol, above objectives cannot be achieved.
For another example, in a country, operator A is strong and has a relatively large user base but a relatively heavy network load In order to expand its services and improve user experiences, operator A decides to purchage the network of operator B so as to achieve the objective of network resource sharing. Though operator A and operator B belong to the same country, they have different Mobile Network Codes (MNCs), therefore for a terminal user using an issued SIM card, he/she is not capable of registering on not only the network of operator A but also the network of operator B by using an existing network searching method in the case that network parameters of a network of operator B are not modified.
When the above two sides sign a network resource sharing agreement or one side acquires the other, in the case that the network side is not modified, a user of a terminal having a commercially-available and issued SIM card, completely according to an implementation method of an existing agreement, can only preferentially select a home network specified by his/her SIM card, i.e., an SIM card issued by operator A can only be preferentially registered on the network of operator A while an SIM card issued by operator B can only be preferentially registered on the network of operator B. This will result in a decrease in utilization rate of a network and cannot solve the problem of network loads, and it is difficult to implement network sharing and network merger, thus affecting user experiences; moreover, if network sharing is implemented by modifying parameters in network side, huge maintenance and repairing cost will be taken.